1. Field of the Invention
The subject of the invention is a process for the production of coherent monochromatic radiation (laser light), the frequency of which can be changed, by means of a dyestuff laser which consists of a reservoir for the dyestuff solution and an energy source, associated therewith, which is capable of exciting the dyestuff solution to produce an emission, the radiation produced being in the wavelength range of 420-480 nm.
2. Discussion of the Prior Art
A laser is a light intensification device by means of which it is possible to produce coherent monochromatic light of a high spectral and geometric intensity density. The laser consists of an optical resonator which contains the liquid laser-active material in a thin-walled quartz cylinder. The cylinder is usually part of a closed system through which the dyestuff solution is circulated by pumping whilst the laser is in operation. This avoids localised overheating, which leads to optical inhomogeneities.
The excitation of the dyestuffs is effected with the aid of energy sources, by means of electrons or light, and the dyestuff laser can also be excited by a gas laser, for example a nitrogen laser or argon laser.
The excitation, which is also termed optical pumping, has the effect of raising the electrons of the molecule of the laser dyestuff from their normal state to a high energy state, from which a radiation transition takes place. If the number of molecules present in the excited state exceeds that of the molecules in lower states, this gives rise to stimulated transitions, by means of which the light is intensified in the optical resonator.
If one of the laser mirrors is partially transparent to light, a part of the radiation leaves the apparatus in the form of a laser beam. Dyestuffs which can be excited particularly easily exhibit the phenomenon of "super radiance" with highly effective excitation. This can be observed, for example, if a quartz cell containing the solution of such a dyestuff is placed in the beam of a nitrogen laser. The solution then emits laser light without being located between resonator mirrors.
A considerable advantage of the dyestuff laser compared with solid or gas lasers is its ability to supply laser radiation of a frequency which can be changed. Because of the width of the fluorescence band of the dyestuffs employed, dyestuff lasers can be so tuned, by inserting a frequency-selective element, for example a reflection grating or a prism, that laser light is emitted at any desired wavelength within the entire fluorescence band of the dyestuff.
Although a large number of suitable dyestuffs has already been proposed, there is, nevertheless, still a considerable lack in many regions of the visible wavelength range of compounds which give a very high degree of effectiveness of the laser.